Substantial sound or noise sources in a motor vehicle may include the internal-combustion engine itself as well as the connected drive components, such as crankshaft, drive shaft, and also the exhaust installation, tire noises, etc. One of the principal sources of noise in a motor vehicle are shafts driven from a drive unit or situated therein. These include the crankshaft, the Cardan shaft, the drive shaft, etc. Internal-combustion engine drive units have, in driving operation, deviations from a predetermined desired turning rate in many or all turning rate zones. Such rotation irregularities or turning-rate disturbances, are caused, for example, by non-uniform combustion in a one-cylinder configuration or by "dropping out" of one cylinder in a multicylinder configuration. They typically cause undesired interference vibrations of the off-drive shaft, especially of the crankshaft, which are transferred to other components of the vehicle and often result in a troublesome noise level.
Some systems have been developed for reduction of noise levels associated with a vehicle during its driving operation and experienced by the vehicle occupants. For example, known systems for noise reduction in a vehicle by active vibration damping include DE 39 39 828 C2 and EP 0 372 590 B1. These documents describe systems that detect the phase and amplitude of undesired vibration from all the sound sources and superimpose an opposite vibration to the source. For example, when the phase of a vibration and amplitude is detected from the vehicle body work, the system superimposes an equal-amplitude additional counter vibration. These systems require an additional corresponding vibration source which transfers the counter vibrations, for example, to the vehicle body-work. The systems for active vibration damping described in the publications DE 41 41 637 A1 and G 91 04 812 U1 operate in substantially the same fashion.
Other documents, DE 36 23 627 A1 and DE 32 30 607 A1, describe methods for monitoring the turning-rate behavior in the drive-line of an internal-combustion engine to detect rotation irregularities. From these detected irregularities, a control arrangement generates signals for controlling a correcting element, possibly in the form of a slip coupling or a three-phase current electric motor where the coupling or rotor of the electric motor is coupled with the crankshaft of the internal-combustion engine. Further, DE-OS 30 05 561 discloses a vibration damping system with an eddy current brake utilized as the correcting element. The vibration damping system disclosed in publication DE 41 00 937 A1 measures possible rotation irregularities of a crankshaft and damps these irregularities with an alternating-current synchronous motor.
Patent Abstracts of Japan, Volume 4, No. 29 (M-002), Mar. 14, 1980, disclose a device for active vibration damping of an internal-combustion motor, the crankshaft of which is equipped with a flywheel. A magnet yoke grips the flywheel in a small zone of the flywheel circumference. The magnet yoke and the flywheel together provide an eddy-current brake utilized as a correcting member.
Other known systems, as noted in the following documents, are directed to partial aspects of active vibration damping. For example, EP 70 553 B1 describes an electrical machine for influencing the turning rate of a gas turbine and DE 453 179 A1 describes a device for monitoring the turning rate of a turbine off-drive shaft in a current-producing generator.
A principal disadvantage of these known vibration-damping systems is the requirement of additional relatively complicated vibration sources for the generation of counter vibrations. The success of noise suppression depends strongly on the location, the form and the material of the vehicle surfaces upon which the counter-vibrations are applied which further complicates such systems. Furthermore, the aforementioned correcting members for influencing shaft movement of a rotating shaft require great expenditures of space due to their structural size.